Magnetron modulator



Dec. 2, 1941. UNDER 2,264,851

MAGNETRON' MODULATOR Original Filed Aug. 20, 1957 3 Sheets-Sheet l Dec. 2, UND

MAGNETRON MODULATOR Original Filed Aug. 20, 1937 3 Sheets-Sheet 2 nv VENTOR U-Sbape m I8! May 7 2 ATTO/k/VEY Dec. 2, 1941. E, G, LINDER MAGNETRON MODULATOR I s Shets-Sheet 3 Original Filed Aug. 20, 1937 AV VENTOR .4 TTORNE r By Fines/6 6.

Patented Dec. 2, 1941 TE rr MAGNETRON MODULATOR Ernest G. Linder, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Original application August 20, 1937, Serial No. 160,003. Divided and this application May 24,

1939, Serial No. 275,362

' affected by a slight relative movement of the 4 Claims.

This application is a division of my copending application Serial No. 160,003, filed August 20, 1937, for a Magnetron modulator, which in turn is a division of my application Serial No. 61,679, filed January 31, 1936, entitled Magnetron modulator, which issued as U. S. Patent No. 2,110,449 on March 8, 1938 and which is assigned to the same assignee as the present application.

My invention relates to a magnetron modulator. More particularly, my invention relates to the modulation of magnetrons by moving the anode with respect to the cathode, or by moving both electrodes with respect to the permanent magnetic field of the magnetron.

A magnetron is a thermionic tube including one or more anodes, a cathode, and a magnetic field. The lines of force of the field are substantially parallel to the cathode. The electrons from the cathode follow a curved path 2 which may be illustrated by Figure I The curved or circular path is due to the forces exerted on the electrons by the magnetic field, the anodes 5, 1, and the cathode 3.

In contrast to the magnetron, an ordinary triode has a cathode, grid, and anode. N0 magnetic field is required. The electrons travel in a substantially straight line from the cathode to the anode. The number of electrons which reach the anode is normally determined by the spacing of the electrodes, and the relative grid, anode, and cathode potentials.

I am aware of ordinary electron tubes in which the electrodes have been relatively movable. The

movement of electrodes in such tubes has slightly varied the number of electrons reaching the anode, or the amplification factor if a triode is used. In the case of a diode or triode, relatively small movement of the electrodes will have a secondary effect on tube operation.

The operation of a magnetron is especially suited to modulation by relative movement of electrodes or of electrodes with respect to the magnetic field. Since the magnetron is used at ultra-high frequencies, the capacity between the anodes is of primary importance. A slight relative movement will have a very large effect on the operating frequency. Furthermore, the circular path of the electrons makes it possible to completely stop the flow of electrons to one anode and to greatly increase the electron flow to the other.

Since the electron path is dependent upon the lines of force of the permanent magnetic field, the operation of the magnetron will be greatly electrodes with respect to the field. By way of example,'the effect of moving the anodes with respect to the cathode is illustrated in Fig. 1' and Fig. 1. Other types of relative movement will produce large changes in anode current. These changes are due to the characteristic magnetron operation.

One of the objects of my invention is to modulate a magnetron by changing the relative spacing of the cathode and anode electrodes.

Another object is to modulate a magnetron by moving thecathode and anode electrodes with respect to the magnetic field.

Another object is to change the relative spacing i of the magnetron electrodes by means of a sound operated diaphragm.

Another object is to vary the operating frequency of a magnetron by moving its electrodes in a non-uniform field.

A further object is to operate a single magnetron as an oscillator, modulator and microphone.

A still further object is to vary the frequency of a magnetron oscillator by varying the interelectrode capacitance.

An additional object is to provide means whereby a magnetron may be made to generate audio frequency currents.

Reference is made to the accompanying drawings, in which Figure I, Figure I and Figure I are illustrative of'the operation of a magnetron embodying my invention,

Figure II is a schematic diagram of a magnetron oscillator including modulation means,

Figure 1111 is an illustration of a magnetron modulated by a sound actuated diaphragm,

Figure IV is a schematic diagram of a modification of Figure I,

Figure V is a schematic diagram of a magnetron in which the anodes are moved with respect to cathode for frequency modulation,

Figure VI is a schematic diagram of a magnetron in which the tube and electrodes are moved with respect to a magnetic field of nonuniform characteristics,

Figure VI represents the anodes and the electromagnet for producing the non-uniform field of Figure VI,

Figure .VI is a plan view of the tube moving means shown in elevation in Figure VI,

Figure V1 is a plan View of the pivotal mounting and biasing spring shown in elevation in Figure VI,

Figure VII is a schematic diagram of a magnetron similar to Figure VI in which the tube moving means is a sound actuated diaphragm, and

Figure VIII is a modification of the apparatus of Figure VII.

Throughout this specification similar reference numerals will be used to designate similar parts. In Figure II, within an evacuated glass envelope I are mounted a cathode 3 and a pair of anodes 5, 1. The anodes are connected to a pair of lead Wires II, I3. A conductor I5 connects the lead wires. This conductor I5 and the anodes 5, 1 form a resonant circuit.

The lead wires I I, I3 may form a transmission line which may be connected to a dipole antenna or the like. The negative terminal of an anode battery I1 is connected to the cathode 3. The positive terminal of the anode battery is connected to a bridging conductor I9 which is suitably located on the leads I I, I3.

A U-shaped magnetic core 2| is energized by a coil 23 and a battery 25. Suitable jaws (not shown). are attached to the pole pieces of the core 2| to clamp the envelope I. The magnetic lines of force between the pole pieces surround and are substantially parallel to the cathode 3. The arrangement thus far described may be operated as a magnetron oscillatorj A series of corrugations 21 are formed in the section of the envelope adjacent the lead-in of the transmission wires I I, I 3. A connecting link 29 is fixed to the end of the envelope adjacent the corrugations 21. A magnetic armature 3| is fastened to the end of the link 29. An electromagnet 33 is suitably positioned with respect to the armature 3|. The winding of the electromagnet is serially connected to a local battery 35 and a microphone 31.

The corrugations 21 offer sufiicient flexibilty to the envelope I to permit movement of the corrugated end of the envelope with respect to the portion clamped by the jaws attached to the magnetic core 2I. A slight movement of the corrugated end which also supports the lead wires II, I3 causes a substantial movement of the anodes 5, 1 with respect to the cathode 3. This movement results in a change of electron distribution represented by Figures I to 1. This change will modulate the normal electron flow.

While I have illustrated the electromagnet 33 and microphone 31 as a convenient means of flexing the tube to effect modulation, it should be understood that other means may be employed. For example, a sound actuated diaphragm, a mechanical movement for telegraphic signalling, or amplifiers may be used.

In Fig. III, the circuit is representative of a magnetron microphone-amplifier. In this device the magnetron operates as a microphone and also as an amplifier, although amplification is not essential. The leads II, I3I are connected to the primary 39 of the push-pull transformer 4!. The anode battery I1 is connected to the center tap of the primary 39. The secondary 43 of the transformer represents the output of the device.

In place of the electromagnetic motor of Fig. II, a sound operated diaphragm 45 has been connected to the link 29. A movement of the diaphragm is transmitted through the link 29 to the flexible end of the envelope I. The movement of the envelope in turn varies the relative position of anodes and cathode. This alters the electron distribution and hence the current fiow through the primary 39.

A modification of Figure II is illustrated in The cathode is energized by a battery 9.

Figure IV. This modification consists primarily in substituting a flexible metal section 41 in place of the corrugated glass section of envelope I. As is known to those skilled in the art, a suitable metal may be attached to glass by sealing. The seal offers an airtight bond between the glass envelope I and the metal envelope 41. The free end of the metal envelope includes a glass insert 49 through which cathode leads may be brought.

with respect to the anode electrodes 5, 1.

In this modification, the cathode 3 is moved The electromagnetic motor device represented by armature 3I and magnet 33 has been connected through links 5|, 53 and lever 55. The lever 55 is pivoted at 51. The single link 29 of Figure II may be used in place of the links and lever. Likewise, the diaphragm 45 of Figure III may be substituted for the electromagnetic motor.

The schematic circuit of Figure IV represents a combined magnetron oscillator, amplifier and microphone. Instead of modulating the magnetron oscillator, the connection of this figure may be arranged similarly to Figure 111 with a resulting microphone, push-pull amplifier action.

A further modification of Figure I is shown in Figure V. In this figure, the tube envelope I is entirely rigid. Instead of flexing the envelope, armatures 6|, 63 are fastened to the lead wires II, I3. The armatures are attracted or repelled by forces generated by the electromagnets 65, 61. Various movements of the anodes may be obtained by proper phasing of the exciting currents. The spaces between the armatures 6 I, 63 and the walls of the envelope are suflicient to permit free movement of the armatures. The bridging conductor 69, which may be. employed in a magnetron oscillator, has sufficient length and fiexibility to permit movement of the lead wires I I I3.

Since the anodes 5, 1 are attached to the lead wires, they may be moved with respect to each other, or with respect to the cathode 3. If the magnetron is oscillating as a negative resistance device, the oscillatory frequency is inversely proportional to the capacity between the anodes;

; therefore, the movements of the anodes with respect to each other will substantially vary their capacities and the oscillatory frequency. If the magnetron is oscillating as an electronic oscillator, variations in relative anode spacing will vary the amplitude of oscillations. Thus, the magnetron oscillator of Figure V may be frequency modulated by impressing currents of the desired modulation frequency on the electromagnets 65, 61.

The arrangement of Figure V may be employed as a microphone-amplifier instead of an oscillator. As an amplifier, the bridging conductor may be omitted. In both cases, the magnetic field is used. The electromagnet structure 2|, 23, 25 of Figure II is suitable for this purpose. A U-shaped permanent magnet may be used, as shown in Figure V.

Instead of using the arrangement of Figure V as a microphone-amplifier combination, this device may be used to generate audio frequency currents. In the generation of audio frequency currents, the microphone 31 is omitted. A portion of the output currents, in the proper phase, is fed back to the exciting magnets 65,51. The feedback currents may be amplified by a triode or the like. The frequency of the audio currents can be controlled by adjusting the natural frequency of vibration of the anodes 5, 1, armatures GI, 63 and lead Wires II, I3.

Figure I represents a magnetron oscillator 01' end of the magnetron by a link IilI. Sound imamplifier which is moved as a whole by the modulation means. The anode and cathode electrodes are moved through a non-uniform magnetic field. Since the frequency of the oscillatory currents, or the amplification, depends upon the magnetic field strength, modulation will be effected by the relatively varying field. This arrangement is best adapted to the electronic mode of oscillation. I

In Figure VI, the envelope I is suitably fastened to a pivot member I I. The pivot member II is pivotally supported by a yoke member I3. One or more biasing springs I are connected between fixed studs 11 on the yoke 73 and the pivot member to yieldably position the tube. These biasing springs may be helical in form, similar to the hair spring on a watch.

The electromagnetic system of this figure differs from the preceding figures. In the preceding figures, the pole pieces of the core 2I were of normal uniform shape and produced a substantially uniform field. The pole pieces I9 for this embodiment of my invention are illustrated in Figure VI The effect of the slanting pole pieces "I9 is to produce a more dense magnetic field between the near points and less dense between the more widely spaced points. Movement of the anodes 5, I and cathode 3 in the nonuniform field will be equivalent to, varying the field. This variation modulates the anode current or varies the frequency of oscillation.

In place of slanting pole pieces, various shape pole pieces may be used. For example, a V or inverted V shaped pole piece or a conical shape will have the required non-uniform field. Where the field has a rate of variation which is uniform with respect to movements on either side of the cathode, push-pull modulation may be produced.

The non-uniform field may be used for purposes other than modulation. For example, a permanent magnet may be substituted for the electrical one, and the operating frequency of the magnetron varied by moving the magnet with respect to cathode and anode. Such a system lends itself to portability and simplicity of frequency adjustments.

One means for moving the magnetron of Figure VI is illustrated as an electromagnetic driver 8|. The driver is shown in plan view in Figure VI and in elevational view in Figure VI A pair of arms 83 are rigidly secured to the envelope I. A magnetic armature 85 is secured to the ends of these arms by soldering, welding, or the like.

The biasing springs normally position the armature 85 in the center of the air gap of a netic core 81. The air gap is of sufficient width to permit the armature to freely oscillate within the gap when the magnet is energized. The energizing means includes the field coil 89, battery 9I, and microphone 93. Amplifiers and lever actions may be employed in place of the direct drive shown.

A modification of Figure VI is illustrated in Figure VII. The essential difference between the apparatus of Figure VI and Figure VII is that the latter has a sound actuated diaphragm 95 to actuate the magnetron with respect to the non-uniform field. This field is produced by a magnet which has slanting pole pieces I9 similar to those shown in Figure VI The diaphragm 95 may be a cone of suitable size. A flexible strip 91 of leather or cloth connects the cone to a rigid supporting ring 99. The center of the cone is connected to the movable pressed on the diaphragm actuates the magnetron which is pivotally mounted as previously described. This combination may be used as a microphone, microphone-amplifier, or oscillator, modulator and microphone.

In the embodiment of my'invention shown in Figure VIII, the magnetron is mounted so that it maybe rocked about the axis of envelope I. A pair of metal rings I83 are clamped at the ends of the envelope I. A pair of wires I05 are attached to each of the rings. These pairs of wires terminate in supports I01.

The pairs of wires and their connections act as a torsional balance. The suspended magnetron may be rocked about the axis of its envelope I. In this figure, the batteries and connecting leads have been omitted. The magnetron may be connected and adjusted for generating, amplifying, oscillating, or modulating currents.

The means for rocking the tube may be a diaphragm, motor, or the like. For purposes of illustration, a sound actuated diaphragm is shown. The diaphragm 95 is coupled to the envelope I by suitable links IEII, I09. The force applied through these links rotates the magnetron about the axis of envelope I. The field in the present instance is of the uniform type. Normally, the magnetic lines of force are substantially parallel to the cathode 3. As the magnetron is rocked back and forth, the relative angular relation between the electrodes and the magnetic lines is varied. This variation alters the electron fiow and thereby modulates the output.

Thus I have described and illustrated several embodiments of my invention by means of which a magnetron may be used as a microphone, microphone amplifier, modulated oscillator, modulator, or audio frequency generator, Various elements of each of the several arrangements may be added to or substituted for elements of the other combinations. For example, a diaphragm may be substituted for the electromagnetic driving motors, and vice versa.

I claim as my invention:

1. An electronic device comprising an evacuated tube, a linear cathode electrode and an anode electrode therein, said anode electrode being resiliently mounted in said tube for motion with respect to said cathode, a magnetic armature connected to said anode, an electromagnet facing and adjacent to said armature, and means for producing a magnetic field whose lines of force surround and are substantially parallel to said cathode electrode whereby electrons follow curvilinear paths about said cathode which are tangent to said anode in its normal position.

2. A magnetron oscillator comprising an evacuated tube, a cathode electrode and a pair of anode electrodes concentrically positioned within said tube, said anode electrodes being resiliently mounted for motion with respect to said cathode, an oscillatory circuit in said tube including said anode electrodes, a magnetic armature connected to each of said anode electrodes, an electromagnet facing and adjacent to each of said armatures, and means for producing a magnetic field parallel to and surrounding said cathode electrode.

3. A magnetron oscillator comprising an evacuated tube, a cathode electrode and a pair of anode electrodes concentrically positioned within 'said tube, said anode electrodes being flexibly field whose lines of force surroundand are substantially parallel to said cathode so that electrons emitted from said cathode follow curvilinear paths within said anodes, a flexible mounting for each of said anodes, a magnetic armature connected to each of said anodes, and an electromagnet facing and adjacent to each of said armatures so that upon movements of said anodes towards and away from said cathode large numbers of electrons in one position and substantially no electrons in the other position impinge upon said anodes.

ERNEST G. LINDER. 

